The present invention relates to a fuel filter and to a process for producing such a filter. In this specification, the term xe2x80x9cfuelxe2x80x9d means any liquid hydrocarbon from crude oil to fully refined, and xe2x80x9cfilterxe2x80x9d means a solid for contact with fuel before combustion to act on or clean the fuel to reduce noxious emissions from subsequent combustion.
It is well known to use a post-combustion catalytic converter to reduce noxious emissions from internal combustion engines. Typically, such converters have a honeycomb substrate of cordierite, which is a high-temperature ceramic. This substrate is plated with a catalyst of platinum material over a porous layer of aluminum oxide. Because of the expensive materials required and the complex structure, such converters are very expensive to produce. This is a major factor in limiting the spread of their use with consequent major adverse implications for the environment.
Some pre-combustion catalytic converters have been described in the art. However, they do not appear to have been implemented to a significant extent in practice, apparently because they are either not effective or are difficult and expensive to manufacture and maintain.
U.S. Pat. No. 3,682,608 (Hicks) includes a very general description of catalysis of fuel before combustion for improved effectiveness. The disclosure concentrates on the mesh structure for additional fuel-catalyzer contact and gives little detail of the catalysis.
GB 1079698 (Carbon Flo.) and WO 90/14516 (Wribro) describe use of a combination of tin, antimony, lead and mercury to provide an alloy which it is claimed catalyses components of fuel for improved efficiency and/or reducing toxicity of the exhaust gases. However, these arrangements do not appear to be particularly effective. ZA 644782 (Broquet) describes use of this type of alloy in the form of pellets immersed in the fuel tank.
A pre-combustion catalytic converter having a platinum catalyst is described in U.S. Pat. No. 5,092,303 (Brown). The catalyst is heated by an electric heater and causes cracking of liquid hydrocarbons in contact with it. It is not clear how effective the converter is, however, it appears to be expensive to produce because of the materials used and the need for a heater and associated control devices.
Thus, while it has been apparent for some time that use of a cleaner fuel would be a simpler way of obtaining improved emissions than use of a post-combustion catalytic converter, heretofore filters to clean fuel have not been used in practice because of lack of effectiveness for various reasons. There is therefore an urgent need for an effective fuel filter for pre-combustion action to cause cleaner emissions. The invention is directed towards providing such a filter.
According to the invention, there is provided a fuel filter for an internal combustion engine, the filter comprising an intermetallic compound.
Preferably, the compound comprises noble metals. The filter can thus attract fuel trace metal ions in an electrochemical displacement reaction.
In this specification, the term xe2x80x9cintermetallic compoundxe2x80x9d means a compound of alloys that is formed when atoms of two metals combine in certain proportions to form crystals with a different structure from that of either of the metals. Further, the term xe2x80x9cnoble metalsxe2x80x9d means metals such as gold, silver, platinum, tin and antimony which have a relatively positive electrode potential, and which are more noble than the trace metals being removed such as calcium, sodium, or iron. By reducing such trace metals in the fuel, the combustion process is more efficient, resulting in cleaner emissions.
In one embodiment, the filter comprises an intermetallic of tin and antimony. Preferably, the tin atomic composition is in the range of 39.5% to 57%. In one embodiment, the tin and antimony are substantially equiatomic.
It has been found that such compositions are particularly effective at providing the galvanic potential for attraction of the trace metals.
In one embodiment, the filter comprises intermetallic particles. The particles may have an average diameter in the range of 1xc3x9710xe2x88x926 m to 1xc3x9710xe2x88x924 m. This is a particularly effective way of providing the filter. Small particles have a high surface area per unit volume and thus there is very effective attraction of the trace metals. The particles may be contained in a fluidised bed or in a column, or indeed may be added to fuel and later removed.
In another embodiment, the filter comprises a porous structure. This is a convenient and effective implementation, for example, for use in a refining process.
Preferably, the filter has a porosity in the range of 30% to 50%, and preferably has permeability of 1xc3x9710xe2x88x9213m2 to 400xc3x9710xe2x88x9213m2. The filter ideally has pores with sizes in the range of 2 xcexcm to 300 xcexcm.
In another aspect, the invention provides a process for producing a fuel filter, the process comprising the steps of preparing a formulation of an intermetallic compound. Preferably, the formulation comprises tin and antimony, and preferably the formulation has a tin atomic composition in the range of 39.5% to 57%.
In one embodiment, the step of preparing the compound comprises the sub-steps of preparing a melt, forming the melt into droplets, and rapidly solidifying the droplets to form intermetallic particles. Ideally, an inert atmosphere is provided around the melt to prevent oxidation. Ideally, the droplets are formed by gas atomisation whereby an inert gas breaks up a melt stream into the droplets.
In one embodiment, nitrogen is used for gas atomisation.
In another embodiment, the melt temperature is below a level at which the melt becomes significantly reactive and absorbs and/or reacts with oxygen.
In one embodiment, the particles are bonded by sintering to form a porous filter structure.
Preferably, the melt comprises tin and antimony and the sintering takes place at a temperature in the range 300xc2x0 C. to 425xc2x0 C. for a time duration of 20 to 40 minutes, and preferably the sintering temperature is approximately 370xc2x0 C. and the time duration is approximately 30 minutes.
In one embodiment, a pore forming agent is added prior to sintering. The pore forming agent is preferably stearic acid.
The filter produced by the process may be in the form of an integral porous structure, it may be formed by deposition of the formulation onto a porous substrate, or it may comprise particles having said formulation and a size in the range of 1xc3x9710xe2x88x926 m to 1xc3x9710xe2x88x924 m.
According to another aspect, the invention provides a method of filtering or cleaning fuel comprising the steps of bringing the fuel into contact with an intermetallic compound.
In one embodiment, the filter comprises noble metals, preferably, a tin and antimony stable intermetallic compound.